Structural quality of (SimGen)(N) superlattices grown on an Si(001)-2 x 1 surface at different temperatures (300-500 degrees C) by molecular beam epitaxy was characterized by reflection high energy electron diffraction, X-ray diffraction, Raman scattering and high-resolution transmission electron microscopy. Asymmetric intermixing is observed, in which the Si-on-Ge interface is less abrupt than the Ge-on-Si interface due to Ge segregation into the growing Si overlayer. It is found that the degree of intermixing and crystalline quality depends on the growth temperature. Experimental evidence shows that significant intermixing due to thermal diffusion of Ge atoms into the growing Si layers occurs at 500 degrees C.